Dry sprinklers are used in areas that are exposed to freezing conditions, such as in freezers or outdoor walkways. In some dry-pipe systems, fluid supply conduits are positioned in a space in which the fluid in the fluid supply conduit is not subject to freezing. A dry sprinkler is attached to the fluid supply conduit and extends into a space in which the fluid would otherwise be subject to freezing.
A typical dry sprinkler comprises a sprinkler head, a tube, a pipe connector at an inlet end of the tube that connects the inlet end to a pipe network of a fire suppression system, a plug seal at the inlet end to prevent water from entering the tube, and an actuating mechanism to maintain the plug seal at the inlet end. Typically, the sprinkler head is attached to an end of the tube that is opposite to the inlet end of the tube. Also, the tube section is conventionally vented to the atmosphere to allow drainage of any condensate that may form in the tube.
Examples of dry sprinklers are generally disclosed in U.S. Pat. No. 5,775,431 to Ondracek, and in U.S. Pat. No. 5,967,240 to Ondracek. As shown generally in these patents, the actuating mechanism of a dry sprinkler can be a rod or other similar structure that extends through the tube between the sprinkler head and the inlet end to maintain the plug seal at the inlet end. The actuating mechanism includes a thermally responsive support element at the sprinkler head that supports the rod and, therefore, the plug seal at the inlet end. In some dry sprinklers, the tube is also sealed at the sprinkler head end of the tube and the actuating mechanism is supported at the sprinkler head end by a seal cap that is supported by the thermally responsive support element. In such arrangements, the space in the tube between the seal cap and the plug seal can be filled with a pressurized gas, such as dry air or nitrogen, or with a liquid, such as an antifreeze solution. When an elevated temperature occurs, the thermally responsive support element fails, releasing the plug seal (and also any lower seal at the sprinkler head end of the tube) to allow water from the fluid supply conduit to flow into and through the tube to the sprinkler head, whereupon the fluid is distributed by the sprinkler head.
Conventional dry sprinklers are fabricated using a rigid tube having a seal at the inlet that is separated from the thermally responsive support element of the sprinkler, which is intended to be positioned in an area exposed to freezing conditions, such as an area that is not heated. The rigid tube extends into the unheated area from a wet pipe system (located in a heated area) and must be precisely aligned and installed while avoiding various architectural, structural and mechanical obstructions typically found in commercial or industrial buildings.